FIG. 4 schematically illustrates a conventional immersion type wire cut electric discharge machine 1. A wire 11 is drawn from a wire reel 12 arranged on an upper arm 4a, and guided along a brake roller 13 and an upper guide roller 14 to a lower guide roller 15 arranged in a lower arm 4b. A workpiece 3 is placed in a machining liquid tank 2 between the upper and lower guide rollers 14 and 15. Electric discharge is induced between the wire 11 and the workpiece 3 immersed in a machining liquid contained in the machining liquid tank 2, thereby causing the workpiece 3 to undergo electric-discharge machining. This type of wire cut electric discharge machine is suited for a machining operation, such as an end-face machining of a thick plate, that requires a sufficient amount of machining liquid to be supplied to a discharging spot and thus, cannot be properly carried out with a nozzle jet type machine in which machining liquid is injected from a nozzle to a machining part of a workpiece.
The immersion type wire cut electric discharge machine must be constructed so that the lower arm 4b is kept projected into the machining liquid tank 2. The machining liquid tank 2 is placed on an X-Y table 5 and is moved relative to the lower arm 4b. Thus, a sealing structure must be provided at a portion A where the lower arm 4b penetrates a tank wall 6 so that the machining liquid tank 2 is allowed to move relative to the lower arm 4b without causing leakage of the machining liquid.
Specifically, the sealing structure must have a construction such that the machining liquid tank 2 can be moved in a horizontal plane in directions perpendicular to each other with respect to the lower arm 4b.